Rediscovery of the extinct Tule shrew (Sorex ornatus juncencis) in the San Quintin plains: a taxonomic reevaluation after 90 years without new records

摘要

In this study, we investigate the geographic distribution of the Tule shrew (Sorex ornatus juncensis), an endemic subspecies of the San Quintin plains associated with coastal vegetation. Records on this shrew are scarce; herein, we provide knowledge about its current conservation status and report the presence of one Tule shrew specimen, something that has not happened since 1926. The distribution of the Tule shrew is associated with coastal vegetation, limited to the San Quintin plains, with scarce records. Field trips were conducted during 2013-2015 in the San Quintin plains and San Pedro Martir range of the Baja California Peninsula. The sampling effort was 3250 trap nights. One specimen of S. o. juncensis was recorded in association with coastal sage-scrub vegetation and identified following the original description, based on its narrower skull relative to Sorex ornatus ornatus. We used a mitochondrial cytochrome b gene sequence (384 bp) to confirm this identification and compare genetic distances using the Kimura's two-parameter nucleotide substitution model vs. other populations of the ornatus group. We found a genetic divergence of less than 1.0% based on sequences from specimens collected from Sierra San Pedro Martir, El Rosario and Sierra La Laguna. In the locality of the S. o. juncensis specimen collected, the original vegetation consists of patches of coastal scrubs, which cover an area of less than 1 km(2), affected by agriculture and habitat fragmentation. We reallocated the taxonomic level of the Tule shrew inhabiting the plains of San Quintin in the Baja California Peninsula to subspecies as S. o. juncensis based on geographic isolation, morphometric characteristics and coloration differences vs. S. o. ornatus. The population inhabiting San Quintin plains is subjected to strong pressure due to habitat loss.